The goal of this proposal is to use direct experimental approaches to test the predictions of two models of olfactory coding. One model suggests that many low-specificity neural elements represent each odorant and the other model suggests that fewer, more specific olfactory receptors combine to convey information regarding multiple molecular features to characterize each odorant. The low-specificity model predicts no effect of any lesion on the coding of any odorant, while the combinatorial model predicts specific deficits with focal lesions. To test these predictions, we will determine the effects of focal olfactory bulb lesions on the recognition, discrimination, and detection of specific odorants. To that end, our laboratory has been studying the glomerular activity evoked by a large number of systematically differing odorants and we have characterized the response domains that combine to form their unique focal representations. Importantly, we have identified odorant pairs that evoke glomerular patterns differing only by a single response domain. Guided by the locations of these domains, we propose to lesion specific areas of focal glomerular activity of rats and we then propose to apply behavioral tests to reveal their resulting odor perceptions. These experiments should help us understand the mechanism by which the olfactory nervous system codes complex stimuli.